California's Sierra Nevada snowpack is a critical factor in the state's water supply. It also looks like a lot of fun to measure. Below, take a look at winter's snowpack surveys and the results they produced, dating back to the 1950s. Hundreds of sites around California each year are measured to give water resources planners an idea of what California can expect for its water supply. The snow along the 400-mile Sierra mountain range melts in the spring in a traditional wet season, runs off into reservoirs ahead of the state's dry, hot summers and provides about 30 percent of California's water. The snowpack was 186 percent of average for March 1, 2017, according to electronic readings -- that was the highest it's been in years. The state benefited from several strong storms last year that knocked out drought conditions in parts of California after a five-year dry spell, but the state could face another setback without more storms this season. The first survey of 2018 is scheduled for Jan. 3.